Roller mills generally comprise a rotatable grinding table with a substantially vertical centerline and a number of rollers configured for interactive operation with the grinding table and turning about separate roller shafts which hare fixed to a rotatable center shaft which also has a substantially vertical centerline.
A roller mill of the aforementioned kind is known from GB 601 299 A. This known roller mill incorporates a drive unit and a gearing mechanism between a rotatable grinding table and a rotatable center shaft. However, the use of a gearing mechanism results in an energy loss due to the mechanical efficiency of (frictional losses within) the gearing mechanism. Futhermore, gearing mechanisms for roller mills are generally subject to severe load conditions and will normally need replacing several times during the lifetime of a roller mill. Moreover, a disadvantage of the mentioned gearing mechanism is that it is not possible to adjust the relative speeds of the grinding table and the rotatable center shaft so that, for example, the grinding table rotates relatively fast and the rotatable center shaft carrying the rollers relatively slow.